The use of Cathode Ray Tubes and similar equipment where light projected images are displayed on display screens is wide spread throughout industry and many millions of users sit day after day hours on end before display screens feeding information into and taking information out of a computer based system. For long periods of time during such use, the user focuses his eyes on relatively small areas of the display screen. The use of the display screen generates stress on the eye muscles that are peculiar to display screen observation.
The display screen is generally about 20 inches from the users eyes and that distance remains relatively constant throughout. Whereas the distance is set up to be somewhat ideal for the user, because there is very little variation, the same eye muscles are in constant use. This causes a strain on those eye muscles not unlike the strain that occurs e.g., in an arm muscle when a light object is held in an extended position for a long period of time.
Also, the images that are displayed on the screen are produced by patterns of dots or line segments. The images thus produced are not crisp and to the eye are slightly out of focus. The images can be read clearly enough but the eye muscles of accommodation are constantly trying to bring the images into focus. This causes a further eye strain phenomenon which in combination with the stationary muscle strain previously explained, creates an eye problem for the video display screen user that is atypical of eye problems encountered for non-users.
The process used by eye doctors to determine the spectacle correction requirements of the typical patient is quite basic. An apparatus is placed in front of the user's eyes that enables the doctor to rapidly change a wide selection of lenses through which the patient is viewing. Images printed on a test card are placed some distance from the patient and as the patient focuses on these images, the doctor assesses the status of the muscles inside the patients eyes with the use of a retinoscope. He can thus determine which combination of lenses is best suited for the patient i.e., when the eye muscles are at a generally relaxed state.
Whereas the process and the equipment currently available are quite satisfactory for prescribing corrective lenses for the average eye problem, such is not satisfactory for correcting the eye problems of the display screen user. The muscles that have created the eye problem for the display screen user cannot be examined under stress with this equipment.
As it will be understood, the fitting of corrective lenses is basically one of trial and error which is quite satisfactory as long as the problem can be simulated in the doctors office and lenses rapidly changed until the lens combination which is most suitable is found to correct the problem. Without the problem simulator (and as heretofore required for display screen users), the same trial and error method involves the doctors educated guess at what lens correction may work best and having the patient go back to his work station to try it out. This is time consuming, expensive, inaccurate and generally unsatisfactory.